Inspector asset preview API

Current State

The Inspector panel displays DataAsset properties but has no way to show visual previews of assets (textures, models, materials, audio waveforms, etc.).

Tasks:

• Design the asset preview API (IPreviewProvider / IPreviewGenerator interface)
• Define a preview registration system (type -> preview factory mapping)
• Implement default preview providers (texture thumbnails, model wireframe, material swatch)
• Integrate preview rendering into the Inspector panel
• Support thumbnail caching to avoid regenerating on every selection
• Allow custom preview providers from editor plugins

Acceptance Criteria:

• Inspector shows a visual preview area for supported asset types
• Texture assets show a thumbnail of the image
• Model/mesh assets show a wireframe or thumbnail render
• Material assets show a material swatch preview
• Preview providers can be registered by editor plugins
• Thumbnails are cached and reused

Related:

, #11 (closed)